Not applicable.
Not applicable.
1. Field of the Invention
The invention relates generally to the field of wellbore liquid lifting systems used in natural gas producing wellbores. More specifically, the invention relates to methods and apparatus for improving the life of plunger seals used with automatic casing swab liquid lift systems.
2. Background Art
Automatic casing swabs are known in the art for lifting liquids produced from earth formations from within wellbores intended primarily for natural gas production. Wellbores which produce natural gas often produce some liquids, either or both oil and water, and/or gas condensate. Some gas producing wellbores do not flow at sufficiently high rates to be able to entrain the produced liquids and thus remove them from the wellbore. For such wellbores, automatic casing swabs have proven to be a useful and economical way to remove produced liquids from the wellbore. A typical prior art automatic casing swab system is described, for example, in, J. W. Cramer et al., Automatic Casing Swabs: A Production System That Can Add Years of Productive Life to Wells, paper no. 30981, Society of Petroleum Engineers, Richardson, Tex. (1995). The typical prior art system includes a plunger adapted to travel along the inside of a casing in the wellbore. The casing has a plunger stop (xe2x80x9cdownhole stopxe2x80x9d) mounted therein, typically at a position just above the uppermost part of a producing (xe2x80x9cperforatedxe2x80x9d) interval in the casing. The perforated interval corresponds to the earth formations which produce gas and liquids into the wellbore. The plunger includes a traveling valve which enables the plunger to freely fall by gravity through the casing until it reaches the downhole stop. When the plunger reaches the downhole stop, the traveling valve is closed, and seals on an outer surface of the plunger engage the wall of the casing. Formation fluid pressure, including gas pressure, then builds up underneath the plunger and causes it to lift, along with wellbore liquids that are trapped above the plunger. Eventually, the plunger reaches a lubricator/trap disposed above control valves on the well disposed at the earth""s surface. The lubricator/trap is adapted to hold the plunger in place therein until it is determined that it is again necessary to remove liquid from the wellbore.
A limitation of prior art automatic casing swab systems is that the seals which engage the internal wall of the casing are subject to rapid wear, damage, and/or deterioration from infusion of gas and fluids into the seal material. Failure to make a positive seal between the casing and the plunger limits or destroys the effectiveness of the plunger to lift liquid.
It is desirable to provide an automatic casing swab system having longer plunger seal life to increase effectiveness and to reduce operating costs.
One aspect of the invention is an apparatus for improving plunger seal life on a casing swab liquid lift system. The apparatus includes a diameter adapter disposed between an upper end of a wellbore casing and a lubricator adapted to receive a plunger therein. The diameter adapter is configured to provide a substantially constant internal diameter between the lubricator and the upper end of the casing.
One embodiment of the diameter adapter includes an adapter flange having an internal bore sized at its lower end to fit over the upper end of the casing, and at its other end having an internal diameter substantially the same as the internal diameter of the casing. Another embodiment of the diameter adapter includes an adapter sleeve having an internal diameter substantially the same as an internal diameter of the wellbore casing. The adapter sleeve is coupled to a flange. The flange is adapted to seat in a tubing spool coupled to a wellhead. The adapter sleeve has a length selected to enable seating of the flange in the tubing spool and to position a lower end of the sleeve proximate the upper end of the casing.
A method according to another aspect of the invention includes inserting into a wellhead disposed at an upper end of a wellbore casing a diameter adapter. The adapter is disposed between the upper end of the wellbore casing and a lubricator adapted to receive a plunger therein. The adapter is configured to provide a substantially constant internal diameter between the lubricator and the upper end of the casing.
A method according to another aspect of the invention includes retaining a swab plunger in a lubricator adapted to receive it for at least an amount of time to enable entrapped gas and fluids to escape from the plunger seal material.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.